Allowable limits of particulates and noxious gases produced by internal combustion engines, including those produced by diesel engines, are generally regulated by the Environmental Protection Agency (EPA). Manufacturers of such engines have accordingly devised techniques for controlling exhaust emissions, and with regard to particulate emissions many now include within the exhaust system a particulate filter or trap, sometimes referred to as a soot filter. Particulate filters are generally designed to collect particulate emissions within the exhaust stream and either continuously or periodically burn off the collected particulates in a so-called particulate filter regeneration mode. In the particulate filter regeneration mode, the temperature of the filter must typically be above a specified regeneration temperature to ensure thorough burning of the collected particulates.
Particulate filters generally fall into two broad categories; namely active and passive. Active particulate filters conventionally include one or more heaters or heating systems that may be selectively controlled in order to control filter temperature, and, in turn, filter regeneration. Passive particulate filters, on the other hand, rely strictly on the temperature of the exhaust gas produced by the engine to elevate the filter temperature sufficiently for filter regeneration.
So-called “hybrid” vehicles are known and typically comprise an internal combustion engine and an electrical motor/generator system, wherein the vehicle driving power is selectively provided under various operating conditions by either one or a combination of these two power sources. For example, under normal operating conditions with a fully charged electrical system, the vehicle driving power is typically provided as a variable ratio of engine and electrical system power. Under vehicle braking conditions and at times when the electrical system is in need of a recharge, one or more generators is typically responsive to rotation of the driveshaft to recharge or regenerate the electrical system.
In conventional internal combustion engine applications, such as in over-the-road trucks and the like, particulate filter temperature is generally controlled solely by the temperature of exhaust gases produced the engine during normal operation thereof. In generally, particulate filters in such applications are typically designed such that “normal” operation of the engine produces exhaust temperatures at or above the particulate filter regeneration temperature with sufficient frequency and duration to avoid particulate build up within the filter.
However, under certain engine operating conditions, such as extended periods of engine idling, sustained operation at high engine speeds and low output torque, and the like, exhaust gas temperatures produced by the engine can be below the filter regeneration temperature for extended periods of time, thereby allowing build up of particulate matter therein. In hybrid internal combustion engine-electrical motor/generation systems of the type described hereinabove, exhaust temperatures produced under normal operation of the engine in such systems likewise may not achieve the particulate filter regeneration temperature with sufficient frequency and/or with sufficient duration to completely regenerate the particulate filter as often as may be required. As a result, particulate filters in either of these applications may frequently become clogged or plugged, thereby requiring unscheduled vehicle maintenance in order to clean the clogged or plugged element. Particulate filter clogging or plugging may also result in filter failure through generation of excessive temperatures internal to the filter when soot is burned.
What is therefore needed is a system for controlling particulate filter temperature in a manner that encourages frequent and/or complete regeneration of the particulate filter so as to reduce the likelihood of filter clogging or plugging and correspondingly reduce vehicle down time required to service the clogged or plugged particulate filter.